Question

Calculate the concentration of an aqueous solution of Ca(OH)2Ca(OH)2 that has a pHpH of 12.11. Express your answer using two significant figures.

Answer 1

Answer: Concentration of $Ca(OH)_2$  is $5.9\times 10{-4}M$

Explanation:

pH or pOH is the measure of acidity or alkalinity of a solution.

pH is calculated by taking negative logarithm of hydrogen ion concentration.

$pH=-\log [H^+]$

$pOH=-\log [OH^-]$

$12.11+pOH=14$

$pOH=1.89$

$1.89=-\log [OH^-]$

$[OH^-]=0.0129$

$Ca(OH)_2\rightarrow Ca^{2+}+2OH^{-}$

According to stoichiometry,

2 mole of $OH^-$ are produced by = 1 mole of $Ca(OH)_2$

Thus 0.0129 moles of $OH^-$ are produced by =$\frac{1}{2}\times 0.0129=5.86\times 10{-4}$ moles of $Ca(OH)_2$

The concentration of $Ca(OH)_2$  is $5.9\times 10{-4}M$